1. Field of the Invention
This invention relates to a surface lighting device. More particularly, the present invention relates to a frontlight type surface lighting device for emitting a light to a reflective type liquid crystal panel.
2. Description of the Prior Art
An example of this kind of a surface lighting device is disclosed in a Japanese Patent Laying-open No.2000-89225 (G 02F 1/1355) laid-open on Mar. 31, 2000. In such a prior art, by forming a predetermined angle between a longitudinal direction of a linear prism formed in plural on the upper surface of a light guide plate and a vertical direction of a pixel pattern of a reflective type liquid crystal display element, the occurrence of moire fringes due to the interference of the prism and the pixel pattern of the reflective type liquid crystal display element is intended to be prevented.
Meanwhile, another example of a surface lighting device is disclosed in a Japanese Patent Laying-open No.2000-11723 (F21V8/00) laid-open on Jan. 14, 2000. This prior art, not a frontlight type, enables improvement of impact-resistance and low voltage drive by use of a point light source and a stick type light guide body in place of a fluorescent lamp used as a linear light source.
On the assumption that such two surface lighting devices are combined with each other, a frontlight type surface lighting device which is improved in impact-resistance and a voltage drive characteristic and does not cause moirxc3xa9 fringes can be obtained.
However, if a gap is caused between a point light source and a stick type light guide body by the positioning at the time that the point light source and the stick light body are mounted on a substrate, a light leaked from the gap is directly incident to a light guide plate, causing an illuminated line on the upper surface of the light guide plate. That is, the illuminated line appears in the direction orthogonal to the prism due to the light leakage.
Therefore, it is a primary object of the present invention to provide a novel surface lighting device.
It is another object of the present invention to provide a surface lighting device capable of decreasing light leakage occurring between a point light source and a stick type light guide body.
A surface lighting device according to the present invention comprises: a point light source which is fixed on a substrate; a stick type light guide body which receives a light emitted from a light-emitting surface of said point light source from an end surface in the longitudinal direction and emits the received light from a side surface in the longitudinal direction; and a light guide plate which receives the light emitted from the stick type light guide body from a first side surface and emits the received light from an upper surface; wherein one of a fitting concave portion and a fitting protruding portion is formed on a predetermined position of the substrate, the other of the fitting concave portion and the fitting protruding portion is formed on a predetermined position of the stick type light guide body, and the point light source and the stick type light guide body are relatively positioned by fitting the fitting protruding portion into the fitting concave portion.
By fitting one of the fitting concave portion and the fitting protruding portion formed on a predetermined position of the substrate into the other of the fitting concave portion and the fitting protruding portion formed on a predetermined position of the stick type light guide body, a relative position between the point light source and the stick type light guide body is determined. Accordingly it is possible to bring the end surface of the stick type light guide body in the longitudinal direction close to the light emitting surface of the point light source, and therefore it is possible to decrease the light leakage occurring from the gap between the light emitting surface and the end surface in the longitudinal direction.
If the fitting concave portion is formed on the upper surface of the substrate, and the fitting protruding portion is formed on the lower surface of the stick type light guide body, transmission of the light incident to the stick type light guide body is never blocked by the fitting protruding portion.
Meanwhile, if the one of the fitting concave portion and the fitting protruding portion is formed in the vicinity of the point light source, and the other of the fitting concave portion and the fitting protruding portion is formed in the vicinity of the end surface of the stick type light guide body in the longitudinal direction, assembly of the surface lighting device will become easy.
Furthermore, on the assumption that the stick type light guide body is arranged in parallel to the first side surface of the light guide plate, and the light emitting surface of the point light source is arranged outside the second side surface of the light guide plate orthogonal to the first side surface in the vicinity of the point light source, even if light leakage occurs between the light emitting surface and the end surface in the longitudinal direction, optical intensity can be decreased by the time the leaked light is reached to the first side surface of the light guide plate.
It is noted that it will be appropriate a linear prism being in parallel to a line crossing the first side surface and the second side surface is formed on the upper surface of the light guide plate.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.